The goals of Gene Expression in Inflammatory Myopathies are: (1) to characterize patterns of muscle gene expression through the use of DNA microarrays among adult patients with distinct subtypes of inflammatory myopathies and correlate these patterns with clinical phenotypes, and (2) to formulate hypotheses relevant to the pathogenesis of the inflammatory myopathies. High-density oligonucleotide microarrays will be used to assay gene expression in muscle biopsy specimens from patients with inflammatory myopathies. These patients will be phenotypically well described and known to the clinical investigators of this proposal. Data analysis of gene expression profiles will be linked to clinical data to refine disease classification and understand distinctions among and within the major subtypes of inflammatory myopathy. Analysis of differential gene expression will also provide clues to pathogenesis of these disorders. This work may provide further diagnostic approaches to these disorders and contribute to the understanding of their pathogenesis.